全文获取类型
收费全文 | 14066篇 |
免费 | 540篇 |
国内免费 | 61篇 |
专业分类
电工技术 | 278篇 |
综合类 | 24篇 |
化学工业 | 2856篇 |
金属工艺 | 395篇 |
机械仪表 | 378篇 |
建筑科学 | 263篇 |
矿业工程 | 77篇 |
能源动力 | 725篇 |
轻工业 | 1465篇 |
水利工程 | 196篇 |
石油天然气 | 83篇 |
无线电 | 1667篇 |
一般工业技术 | 2948篇 |
冶金工业 | 1590篇 |
原子能技术 | 203篇 |
自动化技术 | 1519篇 |
出版年
2024年 | 42篇 |
2023年 | 202篇 |
2022年 | 636篇 |
2021年 | 686篇 |
2020年 | 447篇 |
2019年 | 454篇 |
2018年 | 601篇 |
2017年 | 559篇 |
2016年 | 532篇 |
2015年 | 328篇 |
2014年 | 514篇 |
2013年 | 970篇 |
2012年 | 588篇 |
2011年 | 764篇 |
2010年 | 605篇 |
2009年 | 600篇 |
2008年 | 542篇 |
2007年 | 432篇 |
2006年 | 367篇 |
2005年 | 285篇 |
2004年 | 255篇 |
2003年 | 239篇 |
2002年 | 198篇 |
2001年 | 154篇 |
2000年 | 159篇 |
1999年 | 160篇 |
1998年 | 368篇 |
1997年 | 241篇 |
1996年 | 261篇 |
1995年 | 232篇 |
1994年 | 189篇 |
1993年 | 175篇 |
1992年 | 148篇 |
1991年 | 156篇 |
1990年 | 117篇 |
1989年 | 115篇 |
1988年 | 133篇 |
1987年 | 113篇 |
1986年 | 89篇 |
1985年 | 116篇 |
1984年 | 99篇 |
1983年 | 107篇 |
1982年 | 102篇 |
1981年 | 91篇 |
1980年 | 79篇 |
1979年 | 56篇 |
1978年 | 49篇 |
1977年 | 57篇 |
1976年 | 77篇 |
1975年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
RJ Wilkinson K Hasl?v R Rappuoli F Giovannoni PR Narayanan CR Desai HM Vordermeier J Paulsen G Pasvol J Ivanyi M Singh 《Canadian Metallurgical Quarterly》1997,35(3):553-557
The diagnosis of infection caused by Mycobacterium tuberculosis is of increased public health concern following increases in the number of cases in developed countries and major increases in developing countries associated with the spread of human immunodeficiency virus (HIV) infection. The specificity of purified protein derivative skin testing for the detection of infection is compromised by exposure to environmental mycobacteria. Examination of sputum detects the most infectious patients, but not those with extrapulmonary disease. The 38-kDa antigen of M. tuberculosis contains two M. tuberculosis-specific B-cell epitopes. We overexpressed the gene for this antigen in Escherichia coli and evaluated the recombinant product in in vitro assays of T-cell function and as a target for the antibody response in humans. The sensitivity and specificity of the antigen as a skin test reagent were also assessed in outbred guinea pigs. We found that 69% of healthy sensitized humans recognize the antigen in vitro, as manifested by both cell proliferation and the production of gamma interferon. Untreated patients initially have a lower frequency of response (38%); this recovers to 72% during therapy. A total of 292 patients (20 with HIV coinfection) and 58 controls were examined for production of antibody to the 38-kDa antigen by using a commercially available kit. The sensitivity of the test in comparison with that of culture was 72.6%, and the specificity was 94.9%. The antigen was also tested for its ability to induce skin reactions in outbred guinea pigs sensitized by various mycobacterial species. The antigen provoked significant skin reactions in M. tuberculosis-, M. bovis BCG-, and M. intracellulare-sensitized animals. The significance of these findings and the usefulness of this antigen in immunodiagnosis are discussed. 相似文献
93.
94.
A two-dimensional cross-section finite difference model is presented to simulate density dependent leachate migration in leaky aquifers. Unlike existing models, a new approach is adopted to couple the groundwater-flow equation and the hydrodynamic dispersion equation with the elimination of the intermediate step of calculating velocities. The concept of the reference density is employed, permitting increased accuracy (over pressure-based models) in the representation of the transport process. The model is then used to study the effect of several hydraulic and transport parameters on the flow pattern and plume migration which are found to be very sensitive to most of these parameters. Equiconcentration and equipotential lines are overlapped to provide a better understanding of the coupling effect. 相似文献
95.
The effect of interface-roughness-related disorder on the electronic and optoelectronic properties of a quantum wire structure are studied. It is seen that the disorder causes strong localization in the quasi-one-dimensional system. While the electronic states are seriously perturbed, the density of states is not affected drastically. Optoelectronic properties as reflected in the interband transition related phenomenon are not found to suffer significant deterioration as a result of the disorder. However, the results suggest that intraband relaxation processes may be seriously affected because of electron (hole) states being localized in different regions of the wire 相似文献
96.
97.
A simple and easily programmable technique is proposed for the second-order analysis of frames. This technique involves the iterative process with modification of the stiffness matrix as well as the load vector in each iteration. Both curvature and sway effects are included. A numerical example is included to illustrate the results. 相似文献
98.
An analytical model for electroluminescence in SrS:Ce AC thin-film electroluminescent display devices is presented. The model incorporates an exact calculation of the electric field and the effect of activator ionization and bulk traps. Activator ionization is needed to explain several features of luminescence behavior in SrS:Ce devices. These features include the second luminescence peak at the trailing edge of the voltage pulse and the time lag between the luminescence and the applied voltage when the applied voltage consists of bipolar trapezoidal pulses and rectangular pulses of low voltage amplitudes. As a mechanism for the ionization of activators, field-assisted tunneling is shown to be more likely than impact ionization by hot electrons. Physical processes are described in terms of rate equations, and field, current, and luminescence waveforms are calculated for one set of device parameters. The calculated and experimental luminescence waveforms agree 相似文献
99.
100.